NodeSets are typically initiated with $rulemap->nodeset(@nodes). NodeSets may be empty. Nodesets are independant of State, but heavily dependant on Rulemap.

insertion, lookup, removal of a single node is O(1). Nodesets are mutable, but union & intersect do not affect the invocant. Nodes are topology-implementation-dependent. In ::Rect instances, nodes are defined as a [$row,$col] array ref. In future instances, a node may be defined as a number, with an entry in an adjacency matrix.